1. Field of the Invention
This invention generally relates to a bicycle front derailleur. More specifically, the present invention relates to a bicycle front derailleur, which is designed to be attached to a seat tube of a bicycle frame and which includes chain dropping prevention part to prevent the chain from falling off the inner side of the smallest front sprocket.
1. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle front derailleur.
Generally, a front derailleur includes a fixed member non-movably secured to the bicycle frame and a movable member movably coupled to the fixed member using a linkage assembly so as to be laterally movable relative to the fixed member. The movable member includes an attachment portion and a chain guide with a pair of cage plates for contacting and moving a chain between the front sprockets. A biasing member normally biases the movable member and chain guide to a retracted position or an extended position relative to the fixed member. The fixed member of the front derailleur of the bicycle is typically mounted onto the bicycle frame adjacent to the front sprockets. Specifically, the front derailleur is usually clamped onto the seat tube of the frame.
The movable member is movable relative to the fixed member by pulling or releasing a shift control cable to move against or due to the biasing force of the biasing member. In particular, the movable member and fixed member usually are interconnected through pivotal links of the linkage assembly, while the control cable is connected to one of the pivotal links. Thus, upon pulling the shift control cable, a torque is applied to the link to move the movable member against the biasing force of the biasing member. Alternatively, when the shift control cable is released, the biasing member applies torque in the opposite direction to cause the movable member to move in the opposite direction. Depending on the arrangement and locations of the cable guides, the cable attachment member of the front derailleur may need to be configured differently for different types of frames. An example of such a front derailleur is disclosed in U.S. Patent Publication No. 2003/0100393. While this derailleur works well, it does suffer from some deficiencies.
One problem with this front derailleur and other typical front derailleurs is that it is possible for the chain to fall off the smallest front chain ring to the inner side, especially if the front derailleur gets out of proper adjustment, when riding on especially uneven terrain and/or when used on a dual suspension bicycle. Accordingly, some front derailleurs have been provided that include a guide portion in order to reduce this problem. For example, Japanese Utility Model Patent No. 2607188 discloses such a front derailleur. This front derailleur is mounted on the bottom bracket of the front crankset using a relatively thin plate. The guide portion is formed on this relatively thin bottom bracket mounting plate. This arrangement generally works well. However, this arrangement does not always perform optimally, especially when used on dual suspension type bicycles.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved bicycle front derailleur. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.